It is a standard practice in an automotive vehicle to power an auxiliary device such as a power-brake force amplifier, a clutch, a central door and window locking system, or the like by the vacuum in the intake of the motor-vehicle internal-combustion engine. In particular modern pollution-control devices frequently lower the intake-manifold pressure, particularly when the engine is idling. Thus, in modern engines it is frequently necessary to provide a separate vacuum pump for the above-mentioned auxiliary devices, or to make them all hydraulic and to provide a separate hydraulic pump therefor. This problem is particularly critical with respect to power brakes, as such auxiliary devices normally require considerable vacuum and at the same time must function even when the engine speed is very low.
U.S. Pat. No. 1,374,491 of Apr. 12, 1921 shows a suction-augmenting device usable immediately upstream of the throttle in an internal-combustion engine. Thus a jet-pump arrangement is provided immediately upstream of the throttle, so that even when the engine is operating at low speeds the suction is effectively amplified. Such an arrangement has proven itself unsatisfactory in practice, as the arrangement considerably blocks the throat or flow cross-section of the air intake for the engine. Thus the suction-augmenting device limits the amount of air that can be taken in even at high engine speeds and correspondingly reduces the top speed for the engine.
In U.S. Pat. No. 2,075,231 of Mar. 30, 1937 an engine is described wherein a pressure sensor in the intake manifold can completely shut off the fuel supply during certain types of engine operation. This patent also discloses a rather complex idle-speed circuit, that is a line which feeds some fuel to the engine even when the throttle valve is almost completely closed, which can shut itself down completely during certain operating conditions. This arrangement does not lend itselt, however, to the operation of any auxiliary devices.
An engine is described in French Pat. No. 1,290,074 of Feb. 26, 1962 wherein the pressure from the intake line is used to control the throttle valve with flow of fuel to the engine. Such an arrangement, however, does not overcome the above-given disadvantages.